Problem: $\dfrac{3}{2} - \dfrac{9}{12} = {?}$
Solution: $ = {\dfrac{3 \times 6}{2 \times 6}} - {\dfrac{9 \times 1}{12 \times 1}} $ $ = {\dfrac{18}{12}} - {\dfrac{9}{12}} $ $ = \dfrac{{18} - {9}}{12} $ $ = \dfrac{9}{12}$